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<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
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<body>

  <h1 class="card"></h1>
  
  <script>
    // padStart和padEnd
    // 1.应用场景一: 对时间进行格式化
    // const minute = "15".padStart(2, "0")
    // const second = "6".padStart(2, "0")

    // console.log(`${minute}:${second}`)

    // 2.应用场景二: 对一些敏感数据格式化
    let cardNumber = "132666200001018899"
    const sliceNumber = cardNumber.slice(-4)
    cardNumber = sliceNumber.padStart(cardNumber.length, "*")
    const cardEl = document.querySelector(".card")
    cardEl.textContent = cardNumber

  </script>

</body>
</html>